KR101548024B1 - 12- process for preparing an 12-alkylene carbonate - Google Patents

Abstract

The invention relates to a process for preparing an 1,2-alkylene carbonate comprising (i) contacting carbon dioxide, an 1,2-alkylene oxide and a carbonation catalyst in a reactor to produce a crude reactor effluent containing carbon dioxide, light components, 1,2-alkylene carbonate and catalyst; (ii) separating carbon dioxide and light components from the crude reactor effluent to form a bottoms stream containing 1,2-alkylene carbonate and catalyst; (iii) distilling the bottoms stream formed in step (ii) to form a first distillation overhead stream containing 1,2-alkylene carbonate and a first distillation bottoms stream containing catalyst, and recycling at least part of the first distillation bottoms stream to the reactor; and (iv) distilling the first distillation overhead stream to form a second distillation overhead stream and a second distillation bottoms stream containing 1,2-alkylene carbonate, and recycling at least part of the second distillation overhead stream to the reactor.

Description

PROCESS FOR PREPARING AN 1,2-ALKYLENE CARBONATE [0002]

The present invention relates to a process for preparing 1,2-alkylene carbonates.

Methods for producing 1,2-alkylene carbonates are known. WO-A 2005/003113 discloses a process for contacting carbon dioxide with an alkylene oxide in the presence of a suitable carbonation catalyst. The disclosed catalyst is a tetraalkylphosphonium compound. This specification discloses that the catalyst used is recycled. This specification further discloses that the performance of the catalyst is very stable if the catalyst is recycled to the production of alkylene carbonates in alcohols, especially monopropylene glycol (1,2-propanediol). US-A 4,434,105 also discloses a process for the preparation of 1,2-alkylene carbonates. Various catalysts have been disclosed. This document also describes that the catalyst can be reused after completion of the reaction.

In the continuous process, the reaction product containing the 1,2-alkylene carbonate and the catalyst must be treated by a work-up process. This work-up treatment generally involves one or more distillation steps to separate the 1,2-alkylene carbonate from the catalyst and other components. WO 00/20407 initiates this walk-up process. According to the first aspect of WO 00/20407, the crude carbonation reactor effluent is treated as follows:

(a) a primary evaporator overhead containing an alkylene carbonate by low temperature evaporation of the crude reactor effluent in an evaporator 20, which may be a wiped film evaporator or a falling film tower; and Forming an evaporator bottoms stream containing the catalyst and recirculating the evaporator bottoms stream to the reactor;

(b) separating the light component present in the primary evaporator overhead to form a secondary evaporator overhead and recycling the light component to the reactor;

(c) distilling the secondary evaporator overhead in a distillation column (30) to form a primary distillation bottom stream containing a primary distillation overhead stream and an alkylene carbonate, Lt; / RTI >

(d) distilling the primary distillation bottoms stream in a distillation column (40) to form a secondary distillation overhead stream and an alkylene carbonate containing secondary distillation bottoms stream, Recirculating;

(e) distilling the secondary distillation overhead stream to form a tertiary distillation bottom stream containing a tertiary distillation overhead stream and an alkylene carbonate, and recycling the tertiary distillation overhead stream to the reactor; And

(f) distilling the tertiary distillation bottoms stream to form a fourth distillation overhead stream and a fourth distillation bottoms stream containing purified alkylene carbonate, and recycling the fourth distillation bottoms stream to the reactor.

Thus, the work-up process according to the first aspect of WO 00/20407 comprises a distillation sequence consisting of at least four distillation stages. Prior to the primary distillation stage, the carbonation catalyst and alkylene carbonate separate into a bottom stream and an overhead stream, respectively. The alkylene carbonate is then separated into a bottom stream in the first distillation stage, an overhead stream in the second distillation stage, a bottom stream in the third distillation stage and finally an overhead stream in the fourth distillation stage. Thus, WO 00/20407 teaches the recovery of a purified alkylene carbonate as a distillation overhead stream, i.e., a top product or distillate, rather than as a distillation bottoms stream.

It is an object of the present invention to provide a process for the production of 1,2-alkylene carbonates from carbon dioxide and 1,2-alkylene oxides using a carbonation catalyst, wherein the reactor effluent is such that the final 1,2- Is to provide a process requiring only a limited number of separation steps to reach the 1,2-alkylene carbonate treated in such a way that it contains no or substantially no impurities and thus is purified.

It has been found that this object can be achieved by a process for the preparation of 1,2-alkylene carbonates which comprises the following steps:

(i) contacting carbon dioxide, 1,2-alkylene oxide and a carbonation catalyst in a reactor to produce a crude reactor effluent containing carbon dioxide, a light component, a 1,2-alkylene carbonate and a catalyst;

(ii) separating the carbon dioxide and the light components from the crude reactor effluent to form a bottom stream containing the 1,2-alkylene carbonate and the catalyst;

(iii) distilling the bottom stream formed in step (ii) to form a primary distillation bottom stream containing a primary distillation overhead stream and a catalyst containing 1,2-alkylene carbonate, Recirculating at least a portion of the stream to the reactor; And

(iv) distilling the primary distillation overhead stream to form a secondary distillation bottoms stream containing a secondary distillation overhead stream and a 1,2-alkylene carbonate, and introducing at least a portion of the secondary distillation overhead stream Recycle to the reactor.

According to the process of the present invention, which may be carried out continuously, only a single distillation treatment must be performed after removal of carbon dioxide and light components from the crude reactor effluent. As demonstrated in the following examples, the 1,2-alkylene carbonate in the first distillation is subjected to an overhead stream distillation and the final 1,2-alkylene carbonate product is separated into the bottom stream in the second distillation, , There was no or substantially no impurities in the final product than the distillation of the 2-alkylene carbonate into the overhead stream in the secondary distillation. As discussed above, the 1,2-alkylene carbonate in the distillation sequence according to the first aspect of WO 00/20407 is removed to the bottom stream in the first distillation, The alkylene carbonate is distilled. Moreover, according to this known embodiment, two additional distillations have to be carried out in order to reach substantially pure 1,2-alkylene carbonates.

More specifically, according to the process of the present invention, any halide compound (e.g., bromohydrin) that can be formed as a byproduct during the reaction is removed from the final 1,2-alkylene carbonate product, It was found that the step can not be interrupted. It has also been found that halide byproducts are recycled to the carbonation reactor together with the catalyst, thereby enhancing the promoting behavior of the system.

In addition to essentially no or substantially no impurities in the final product, another advantage is that in the process of the present invention, the carbon dioxide and the light components are first separated in step (ii) from the crude reactor effluent formed in step (i). This provides a relatively small amount of vapor to be loaded into the next separation step (iii) of the inventive process wherein the bottom stream formed in step (ii) is distilled. As a result, the size of the distillation column in which step (iii) is carried out can be considerably reduced. However, the vapor loading of the separation unit according to the first aspect of WO 00/20407 is relatively large because the alkylene carbonate is discharged overhead with the carbon dioxide and the light components in the primary separation step.

Fig. 1 schematically shows the method of the present invention. Steps (i) to (iv) of the method are each described in more detail below.

In step (i) of the process, the carbon dioxide, 1,2-alkylene oxide and the carbonation catalyst are contacted in the reactor. As shown in FIG. 1, the three components are introduced into the reactor 10 via line 11. Alternatively, the three components may be fed through other lines. For example, the 1,2-alkylene oxide may be fed to the top of the reactor 10 via another line; Carbon dioxide can be fed through another line to the middle of the reactor; The catalyst may be supplied via another line to the bottom of the reactor.

The carbonation catalyst used in the present invention is generally a homogeneous catalyst, but a heterogeneous catalyst may be used. Certain catalysts known to be suitable are homogeneous, phosphorus containing catalysts. Phosphorus is generally not present in elemental form in the catalyst. The carbonation catalyst may be a phosphonium compound. Such catalysts are known for example from US-A 5,153,333, US-A 2,994,705, US-A 4,434,105, WO-A 99/57108, EP-A 776,890 and WO-A 2005/003113. The catalyst is preferably a phosphonium halide of the formula R4PHal, wherein Hal stands for halide and each R is the same or different and can be selected from alkyl, alkenyl, cyclic aliphatic or aromatic groups. The carbonation catalyst preferably contains tetraalkylphosphonium bromide. Suitably, the R group contains from 1 to 12 carbon atoms. If R is a C _1-8 alkyl group, good results are obtained. Most preferably, the R group is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl and t-butyl groups. The halide ion is preferably bromide or iodide. The most preferred phosphonium catalyst is tetra (n-butyl) -phosphonium bromide.

The catalyst can be recycled to the reactor as a solid, especially if it is a phosphonium catalyst. It is also possible to convert the catalyst into a melt and recycle the molten catalyst to the reactor. However, it is preferable to recycle the catalyst to the reactor in the presence of the solvent since the presence of the solvent shows a stabilizing effect on the catalyst. The solvent may be a carbonyl-containing compound, especially an aldehyde, as disclosed in WO-A 2005/051939. More preferably, the solvent is alcohol. Many alcohols can be selected to increase the stability of the catalyst, especially the phosphonium catalyst. Alcohols can be monovalent, divalent or multivalent. Alcohols may include aliphatic C _1-12 chains substituted with one or more hydroxy groups. Also suitable are aromatic alcohols or alkylaromatic alcohols, suitably having from 6 to 12 carbon atoms. Polyalkylene glycols or monoalkyl ethers thereof may also be used. Mixtures may be used.

The alcohols used are C _1-6 mono-alkanols, C _2-6 alkane diols, C _3-6 alkane polyols, such as glycerol, phenol, C _1-6 alkyl substituted phenols, C _6-12 cycloaliphatic alcohols And mixtures thereof. C _2-6 alkane polyols, especially 1,2-ethanediol, 1,2-propanediol, sorbitol and mixtures thereof are very suitable. The use of ethanediol or propanediol shows additional advantages when the alkylene carbonate is converted to an alkylene glycol (alkane diol) and an alkylene glycol is used as the solvent for the catalyst. Sorbitol provides excellent stability to phosphonium catalysts. It may be advantageous to use a mixture of 1,2-ethanediol or 1,2-propanediol and sorbitol.

The 1,2-alkylenediol is preferably used as a solvent for the carbonation catalyst. In this case, the primary and secondary distillation overhead streams contain 1,2-alkylenediol.

When the 1,2-alkylenediol is used as a solvent for the carbonation catalyst, the 1,2-alkylenediol is preferably monoethylene glycol and / or monopropylene glycol. When such a solvent is used, the 1,2-alkylene oxide may be ethylene oxide, the 1,2-alkylene diol may be monoethylene glycol, or the 1,2-alkylene oxide may be propylene oxide, , The 2-alkylenediol may be monopropylene glycol.

The 1,2-alkylene carbonate is preferably used as a solvent for the carbonation catalyst. More preferably, distillation of step (iii) is preferably carried out such that a portion of the 1,2-alkylene carbonate is contained in the primary distillation bottoms stream, wherein the 1,2-alkylene carbonate is then added to the stream Can be used as a solvent for the catalysts contained together. The 1,2-alkylene carbonate allows the used catalyst to be in a liquid form to facilitate transport, e.g., recycle.

It has also been found that the combination of an alcohol and a 1,2-alkylene carbonate exhibits a stabilizing effect on a carbonation catalyst. It is preferred that the secondary distillation overhead stream contains an alcohol, such as a 1,2-alkylenediol, in which case the alcohol is used as a solvent for the carbonation catalyst. Thus, when such alcohols are used, the primary distillation bottoms stream and the secondary distillation overhead stream may be suitably formulated such that the mixture of catalyst, alcohol and alkylene carbonate is recycled to the reactor.

In order to supplement any cracked catalyst, it may be effective to add makeup catalyst. The makeup catalyst may be added at any position of the process in which the catalyst is present. Any makeup catalyst is suitably added to the process via direct addition to the reactor or addition to the catalyst stream to be recycled.

It is convenient that the amount of catalyst in the reactor is expressed as the catalyst mole per mole of 1,2-alkylene oxide. Suitably the process is carried out in the presence of at least 0.0001 moles of catalyst per mole of 1,2-alkylene oxide since the amount of by-products is small. The amount of catalyst present is preferably in the range of 0.0001 to 0.1 mole, more preferably 0.001 to 0.05 mole, and most preferably 0.003 to 0.03 mole per 1 mole of 1,2-alkylene oxide.

The 1,2-alkylene oxide which is converted in the process is suitably a C _2-4 alkylene oxide, preferably ethylene oxide and / or propylene oxide, or a mixture of such C _2-4 alkylene oxides.

The reaction of 1,2-alkylene oxide with carbon dioxide is reversible. This means that the 1,2-alkylene carbonate formed can be converted back into carbon dioxide and 1,2-alkylene oxide. The molar ratio between carbon dioxide and 1,2-alkylene oxide may be as low as 0.5: 1, more preferably 0.75: 1. In view of the reversibility of the reaction, it is preferable to use at least a slight excess of carbon dioxide, for example, 1.0: 1 to 10: 1, more preferably 1.01: 1 to 2: 1, most preferably 1.01: Range. A suitable means for forming an excess of carbon dioxide is to carry out the reaction at elevated carbon dioxide pressure and keep the pressure constant by injecting carbon dioxide. A total pressure in the range of 5 to 200 bar is suitable; The partial pressure of carbon dioxide preferably ranges from 5 to 70 bar; More preferably in the range of 7 to 50 bar, and most preferably in the range of 10 to 30 bar.

In addition to providing the desired excess of carbon dioxide, the operation at the above-described increased pressures is preferred because the reaction is essentially liquid-phase, as the 1,2-alkylene oxide, such as ethylene oxide and propylene oxide, .

The reaction temperature can be selected from a wide range. The temperature is suitably selected in the range of 30 to 300 占 폚. The advantage of a relatively high temperature is an increase in the reaction rate. However, if the reaction temperature is too high, side reactions, such as the decomposition of 1,2-alkylene carbonate into carbon dioxide and propionaldehyde or acetone, the reaction with 1,2-alkylene oxide and optional 1,2-alkanediol Reaction may occur, or undesirable decomposition of the catalyst may be accelerated. Therefore, the temperature is suitably selected from 100 to 220 캜.

Those skilled in the art will be able to employ other suitable reaction conditions. The residence time of 1,2-alkylene oxide and carbon dioxide in the reactor can be selected without undue burden. The residence time can generally vary between 5 minutes and 24 hours, preferably between 10 minutes and 10 hours. The conversion of the 1,2-alkylene oxide is preferably 95% or more, and more preferably 98% or more. The residence time can be adopted depending on temperature and pressure. Also, the catalyst concentration can be varied in various ranges. Suitable concentrations include from 1 to 25 wt%, based on the total reaction mixture. Good results can be obtained at catalyst concentrations of 2 to 8 wt% based on the total reaction mixture.

With respect to the relative amount of 1,2-alkylene carbonate and alcohol, when the latter is used solely as a solvent for the catalyst, one of ordinary skill in the art can vary the ratio in a wide range. Very good results have been obtained by using the weight ratio of 1,2-alkylene carbonate to the alcohol in the range of 1 to 100, especially 2 to 50, more preferably 5 to 25. In view of the undesirable reaction opportunities between the 1,2-alkylene oxide and the alcohol in the reactor, the amount of alcohol is determined by the weight of the 1,2-alkylene oxide, carbon dioxide, 1,2-alkylene carbonate and alcohol present in the reactor It is appropriate to keep it at a relatively low level, for example 1 to 25 wt%. The amount of alcohol is preferably in the range of 5 to 20 wt%.

When the catalyst is recycled to step (i) as part of the solution, it is advantageous if the amount of catalyst present in said mixture recycled to step (i) is relatively high. This means that the yield of the final 1,2-alkylene carbonate product is high while the recycle cost is kept to a minimum. Thus, the amount of catalyst present in the mixture of catalyst and 1,2-alkylene carbonate is preferably in the range of 1 to 90 wt%, more preferably 5 to 75 wt%, based on the total mixture. It has been found that the stability of the catalyst is slightly reduced when the 1,2-alkylene carbonate weight ratio to the catalyst is less than 1, the amount of catalyst being 10 to 40 wt% and the balance being 1,2-alkylene carbonate and, It is most preferred to include.

In step (i) of the process, only one reactor may be used. However, it is also possible to carry out the reaction of step (i) in two or more reactors. In this case, it may be advantageous to provide an optimum amount of carbon dioxide in the reactor by adding or removing carbon dioxide between the reactors. The reactor is suitably carried out under perfusion flow reaction conditions. Even more preferably, a reverse mixing reactor, such as a continuous stirred tank reactor (CSTR) and subsequently a plug-flow reactor, is used. Such combinations are known from US-A 4,314,945.

The carbon dioxide used in the process may be pure carbon dioxide or carbon dioxide containing additional compounds. Particularly suitable carbon dioxide for use in the present invention is carbon dioxide separated in any subsequent steps of the process. The extent to which carbon dioxide is refined depends on the content and nature of the impurities present in the carbon dioxide. A small amount of water may be present in the carbon dioxide fed to the carbonation reactor. For example, water and 1,2-alkylene oxide may be reacted with 1,2-alkylene glycol. The 1,2-alkylene glycols produced in this manner can be used to maintain the desired level of 1,2-alkylene glycol if such 1,2-alkylene glycol is used as a solvent in the catalyst, for example by bleed or The 1,2-alkylene carbonate product can be easily removed from the system.

In step (ii) of the process, the carbon dioxide and the light components are separated from the crude reactor effluent to form a bottom stream containing the 1,2-alkylene carbonate and the catalyst. As shown in FIG. 1, the crude reactor effluent exits the reactor 10 via line 12 and is introduced into separator 20. In the separator 20, the carbon dioxide and the light component are separated. The bottoms stream formed in step (ii) is fed via line 21 to the distillation column 30. It is preferred that at least a portion of the separated light components and / or carbon dioxide is recycled to the reactor 10 (not shown in FIG. 1). The separator 20 may be composed of a plurality of, for example, two gas-liquid separators.

According to the description of the present invention, in addition to carbon dioxide, the light component has a boiling point lower than the boiling point of 1,2-alkylene glycol and 1,2-alkylene carbonate, more particularly not higher than 185 ° C, most particularly not higher than 180 ° C / RTI > Examples of such light components present in the crude effluent from the carbonation reactor may be unreacted 1,2-alkylene oxide and any light impurities formed during the carbonation reaction, such as acetone, propionaldehyde, allyl alcohol and acetaldehyde .

Further, according to the description of the present invention, the overhead stream is obtained at the top or top of the separation apparatus such as a distillation column. Likewise, the bottoms stream is obtained at the bottom or bottom of a separator such as a distillation column. If the distillation column is used as a separation device, this means that the overhead stream can be discharged from the top tray or the tray located below the top tray, and the bottom stream can be discharged from the bottom tray or the tray located above the bottom tray.

In step (iii) of the process, the bottoms stream formed in step (ii) is distilled to form a primary distillation overhead stream and a primary distillation bottoms stream. The primary distillation overhead stream contains 1,2-alkylene carbonate. The primary distillation bottoms stream contains the catalyst. At least a portion of the primary distillation bottoms stream is recycled to the reactor. If the process is operated in series, bleeding can optionally be taken from the recycle stream from step (iii) to step (i). Alternatively, the entire stream may be recycled without taking any bleed from the recycle stream.

1, in the distillation column 30, the bottom stream containing the catalyst derived from the separator 20 and the 1,2-alkylene carbonate is subjected to distillation treatment to produce a primary stream containing 1,2-alkylene carbonate To form a distillation overhead stream, which is fed via line 31 to the distillation column 40. In addition, a primary distillation bottoms stream containing a catalyst and possibly some 1,2-alkylene carbonate is formed, at least a portion of which is recycled via line 32 to the reactor 10. Possibly, a makeup catalyst may be added to line 32 or added to any other suitable location in the process.

In a situation where an alcohol is used as a solvent for the catalyst and the alcohol has a boiling point lower than that of the 1,2-alkylene carbonate, for example when the alcohol used is 1,2-propanediol and the 1,2-alkylene carbonate is propylene carbonate, When the alcohol is 1,2-ethanediol and the 1,2-alkylene carbonate is ethylene carbonate, the primary distillation overhead stream contains 1,2-alkylene carbonate in addition to the alcohol. The primary distillation overhead stream may also contain some light components formed in the distillation column, for example, during distillation near the reboiler of the column.

(Iii) to separate the catalyst and possibly some 1,2-alkylene carbonate from any alcohol and any light components used as the solvent of the catalyst, the 1,2-alkylene carbonate, the method , Those skilled in the art will be able to vary the temperature and tray number without undue burden.

In step (iv) of the process, the primary distillation overhead stream is distilled to form a secondary distillation overhead stream and a secondary distillation bottom stream. The secondary distillation bottoms stream contains 1,2-alkylene carbonate, i.e. the purified final product. At least a portion of the secondary distillation overhead stream is recycled to the reactor. If the process is operated in series, bleeding can optionally be taken from the recycle stream from step (iv) to step (i). Alternatively, the entire stream may be recycled without taking bleed in the recycle stream.

1, the primary distillation overhead stream containing the 1,2-alkylene carbonate from the distillation column 30 in the distillation column 40 is distilled and removed via line 41 To form a secondary distillation bottoms stream containing the 1,2-alkylene carbonate product. In addition, a secondary distillation overhead stream is formed, at least a portion of which is recycled to the reactor (10) via line (42).

In the situation where alcohol is used as a solvent for the catalyst and the alcohol has a lower boiling point than 1,2-alkylene carbonate, the distillation in step (iv) is carried out in such a way that the second distillation overhead stream contains the alcohol and the final 1,2- It should be carried out so that the product of the recarbonate does not contain or substantially contains no alcohol. The secondary distillation overhead stream may additionally contain some light components formed during distillation in step (iii) and / or step (iv) of the distillation column, for example, near the reboiler of the column. If possible, make-up alcohol may be added to line 42 or any other suitable location of the process. The recycle stream from the distillation column 40 may be fed directly to the reactor or may be recycled in another vessel to the distillation column 40 via a recycle stream containing the catalyst from the distillation column 30 and possibly some 1,2- Stream (not shown in FIG. 1). It is preferred that at least a portion of the primary distillation bottoms stream and at least a portion of the secondary distillation overhead stream are mixed before being recycled to step (i).

With regard to the distillation mode which can be carried out in step (iv) to separate the 1,2-alkylene carbonate from any alcohol and any light components used as the solvent of the catalyst, those skilled in the art will appreciate that the temperature and the number of trays .

The 1,2-alkylene carbonates produced in this process can be suitably used for the production of 1,2-alkanediol and dialkyl carbonate. Thus, the method of the present invention preferably comprises the following additional steps:

(v) contacting at least a portion of the secondary distillation bottoms stream formed in step (iv) with an alkanol to obtain a reaction mixture containing a 1,2-alkylenediol and a dialkyl carbonate; And

(vi) recovering 1,2-alkylenediol and dialkyl carbonate.

The alkanol used in the transesterification step (v) is preferably a C _1-4 alcohol. The alkanol is preferably methanol, ethanol or isopropanol. The step (v) may be carried out in the presence of a heterogeneous transesterification catalyst.

The transesterification reaction itself is known. In this situation, it has been found that on heterogeneous catalyst systems, in particular by transesterification on ion exchange resins in which tertiary amines, quaternary ammonium, sulfonic acid and carboxylic acid functional groups, alkali and alkaline earth silicates are impregnated with silica and ammonium exchanged zeolites See US-A 4,691,041 which discloses a process for preparing ethylene glycol and dimethyl carbonate. US-A 5,359,118 and US-A 5,231,212 disclose the use of an alkali metal compound, specifically an alkali metal hydroxide or alcoholate such as sodium hydroxide or sodium methanolate, a thallium compound, a nitrogenous base such as a trialkylamine, Discloses a continuous process for the production of dialkyl carbonates over various catalysts, including selenium, sulfur or selenium compounds and tin, titanium or zirconium salts. According to WO-A 2005/003113, the reaction of an alkanol with an alkylene carbonate is carried out on a heterogeneous catalyst, such as alumina.

Fig. 1 schematically shows the method of the present invention.

Fig. 2 schematically shows a process carried out in the comparative example.

The present invention will be explained more clearly by way of the following examples.

Comparative Example

Fig. 2 schematically shows a process performed in this comparative example. In the reactor 10 shown in FIG. 2, carbon dioxide, 1,2-alkylene oxide and a carbonation catalyst were contacted. These were introduced into the reactor (10) via line (11). The crude reactor effluent was transferred from the reactor 10 to the separator 20 via line 12. In the separator 20, the carbon dioxide and the light components are separated from the crude reactor effluent to form a bottoms stream containing the 1,2-alkylene carbonate and the catalyst, which is passed through line 21 to the primary distillation Column 50 as shown in FIG. The separated hard component and carbon dioxide are partially recycled to the reactor 10 (not shown in FIG. 2).

The method shown schematically in Fig. 2 differs from that of Fig. 1 showing the method of the present invention in the following two aspects.

First, in the primary distillation column 50 of FIG. 2, the bottoms stream containing the 1,2-alkylene carbonate and the catalyst from the separator 20 is distilled to produce a mixture of 1,2-alkylene carbonate and 1 To form a tea distillation bottoms stream, which was fed via line 51 to distillation column 60. A primary distillation overhead stream was also formed, which was entirely recycled to reactor 10 via line 52.

Second, in the distillation column 60 of FIG. 2, the primary distillation bottoms stream containing the 1,2-alkylene carbonate and the catalyst from the distillation column 50 is distilled to produce the final 1,2-alkylene carbonate product To form a secondary distillation overhead stream, which was removed via line 61. [0060] A secondary distillation bottoms stream was also formed, which was all recycled to the reactor 10 via line 62.

The 1,2-alkylene oxide used was propylene oxide which reacted with carbon dioxide to provide propylene carbonate. The carbonation catalyst used is a homogeneous catalyst, i.e., tetra (n-butyl) phosphonium bromide, dissolved in a solution containing propylene carbonate, 20 wt% of the catalyst and 20 wt% of monopropylene glycol. The feeding rate to the reactor 10 was 114 g / h of propylene oxide, 60 normal liters / h of carbon dioxide (molar excess of carbon dioxide than propylene oxide) and 57 g / h of catalyst solution. The pressure and temperature inside the carbonation reactor were 20 bar gauge and 150 ° C respectively. This reactor was a mechanical agitation type autoclave having a capacity of 1 liter.

The light components and carbon dioxide in the crude reactor effluent were removed in two cascade-connected gas-liquid separators (not shown in FIG. 2). The primary gas-liquid separator operated at 24 bar gauge and 60 ° C, and the secondary gas-liquid separator operated at 4 bar gauge and 60 ° C. The light components and carbon dioxide from the primary separator were recycled to the carbonation reactor. The light components and carbon dioxide from the secondary separator were discharged to the incinerator header.

The crude bottoms stream containing propylene carbonate, monopropylene glycol and catalyst from a secondary gas-liquid separator was fed to the first distillation column of the two distillation columns connected in series. The primary distillation column consisted of 17 trays and the feed was a glass Oldershaw column that lie on 10 trays over the bottom reboiler. The bottom temperature of the primary distillation column was 140 ° C and the pressure in the ceiling was 0.030 bar (absolute pressure). The reflux ratio was R / D = 1.6 (i.e., the ratio of the reflux stream to the ceiling product stream). The primary distillation overhead stream contained monopropylene glycol and was entirely recycled to the carbonation reactor via the catalyst recycle vessel (not shown in FIG. 2). In addition, the primary distillation overhead stream also contained some propylene carbonate (about 15 wt%) because propylene carbonate at this temperature and pressure forms an azeotrope with monopropylene glycol. The entire process was operated continuously but no bleed was taken from the recycle stream. The primary distillation bottoms stream containing propylene carbonate and catalyst was fed into a secondary distillation column.

The secondary distillation column consisted of five trays, all of which were glass Oldershaw columns that were not below the feed. The bottom temperature of the primary distillation column was 135 ° C and the pressure in the ceiling was 0.03 bar absolute. The reflux ratio was R / D = 0.3 (ratio of reflux flow to ceiling product flow). The secondary distillation bottoms stream contained a catalyst dissolved in propylene carbonate and the catalyst concentration in the bottoms product was about 25 wt% and was fed to the carbonation reactor through the catalyst recycle vessel described above, which was mixed with the recycle stream from the primary distillation column All were recycled. Although the entire process was operated continuously, no bleed was taken from the recycle stream. The secondary distillation overhead stream contained the final propylene carbonate product.

Example

Fig. 1 schematically shows a method performed in this embodiment according to the present invention. The procedure performed was the same as that performed in the Comparative Example except that the primary distillation column was the same as the secondary distillation column used in the Comparative Example and the secondary distillation column was the same as the primary distillation column used in the Comparative Example did.

Another difference is that the primary distillation bottoms stream containing the catalyst dissolved in propylene carbonate in this embodiment and the secondary distillation overhead stream containing monopropylene glycol (and some propylene carbonate) are all carbonated through the catalyst recycle vessel described above And recycled to the reactor.

Another difference is that the primary distillation overhead stream containing the 1,2-alkylene carbonate (and monopropylene glycol) in this example is distilled in the secondary distillation column. In addition, in this embodiment, the final propylene carbonate product is discharged from the secondary distillation column to the bottom stream, while in the comparative example, it is discharged from the secondary distillation column as an overhead stream.

Comparison between Examples and Comparative Examples

The following table summarizes some impurities and their contents found in the samples taken from the final 1,2-alkylene carbonate products of Examples and Comparative Examples.

table

Comparative Example Example Acetaldehyde (mg / kg) 6 2 Propylene oxide (mg / kg) 1390 One Propionaldehyde (mg / kg) 2 Not detected Allyl alcohol (mg / kg) 6 Not detected Bromohydrin ¹ (mg / kg, as bromine) 18 Not detected ¹ Bromohydrin is a mixture of 1-bromo-2-hydroxy-propane and 2-bromo-1-hydroxy-propane.

The table shows that according to the present invention it is possible to substantially reduce or even completely eliminate the amount of some impurities present in the final propylene carbonate product, more specifically the amount of propylene oxide. It is believed that the propylene oxide is formed through the catalyzed reverse reaction of propylene carbonate to propylene oxide and carbon dioxide, perhaps near the re-boiling of the distillation column. It is believed that other impurities such as acetaldehyde, propionaldehyde, and allyl alcohol are formed by the pyrolysis or promotion reaction of propylene carbonate in the distillation column.

Another impurity is bromohydrin. This is presumably due to the decomposition of the tetra (n-butyl) phosphonium bromide catalyst and subsequent reaction with propylene oxide. In a comparative example, all of these bromohydrins remain in the final propylene carbonate product. In this manner, bromohydrin may interfere with any subsequent processing steps, such as reaction of the 1,2-propylene diol with the propylene carbonate product to yield a dialkyl carbonate, and the like. Thereafter, bromohydrin may remain in the final dialkyl carbonate product. This is disadvantageous when bromine-free dialkyl carbonates are needed in many applications where dialkyl carbonates are used. On the other hand, no bromohydrin was detected in the final propylene carbonate product obtained in the examples.

A further advantage is that in the embodiment the bromohydrin is completely recycled from the secondary distillation column to its carbonylation reactor via its overhead stream. It has been found that the promoting behavior of the system is improved by recycling the halide byproducts to the carbonation reactor with the catalyst. Bromohydrin is believed to be capable of reactivating any deactivated catalyst, possibly in the form of HO-PBu ₄ , to an active catalyst, possibly in the form of Br-PBu ₄ .

Claims (15)

(i) contacting carbon dioxide, 1,2-alkylene oxide and a carbonation catalyst in a reactor to produce a crude reactor effluent containing carbon dioxide, a light component, a 1,2-alkylene carbonate and a carbonation catalyst; (ii) separating the carbon dioxide and the light components from the crude reactor effluent to form a bottom stream containing the 1,2-alkylene carbonate and the carbonation catalyst; (iii) distilling the bottom stream formed in step (ii) to form a primary distillation bottom stream containing a primary distillation overhead stream and a carbonation catalyst containing 1,2-alkylene carbonate and a light component, Recirculating some or all of the primary distillation bottoms stream to the reactor; And (iv) distilling the primary distillation overhead stream to form a secondary distillation overhead stream containing the light components and a secondary distillation bottom stream containing the 1,2-alkylene carbonate, Recirculating part or all of the stream to the reactor Lt; / RTI > The light component is a compound having a boiling point lower than the boiling point of 1,2-alkylene glycol and 1,2-alkylene carbonate except for carbon dioxide, Wherein the 1,2-alkylene oxide is a C _2-4 alkylene oxide,  A process for producing 1,2-alkylene carbonate. The process according to claim 1, wherein the solvent is used in the reactor for the carbonation catalyst, and the solvent is 1,2-alkylenediol. 3. The process according to claim 2, wherein the primary and secondary distillation overhead streams contain a 1,2-alkylenediol. 4. A process according to claim 3, wherein some or all of the primary distillation bottoms stream and some or all of the secondary distillation overheads stream are recycled to step (i). The process according to any one of claims 1 to 4, wherein the light component separated in step (ii), or carbon dioxide, or a portion of the light component and carbon dioxide is recycled to the reactor. The process according to claim 1, wherein the solvent in the reactor is used for the carbonation catalyst, and the solvent is 1,2-alkylene carbonate. 7. The process of claim 6 wherein the primary distillation bottoms stream contains a portion of the 1,2-alkylene carbonate. The process according to any one of claims 1 to 4, wherein the carbonation catalyst contains tetra-alkylphosphonium bromide. 5. The process according to any one of claims 1 to 4, wherein the 1,2-alkylene oxide is ethylene oxide, or propylene oxide, or ethylene oxide and propylene oxide. 3. The process according to claim 2, wherein the 1,2-alkylenediol is monoethylene glycol, or monopropylene glycol, or monoethylene glycol and monopropylene glycol. The process according to any one of claims 2 to 4, wherein the 1,2-alkylene oxide is ethylene oxide and the 1,2-alkylenediol is monoethylene glycol. The process according to any one of claims 2 to 4, wherein the 1,2-alkylene oxide is propylene oxide and the 1,2-alkylenediol is monopropylene glycol. 5. The method according to any one of claims 1 to 4, (v) contacting a part or all of the secondary distillation bottoms stream formed in step (iv) with an alkanol, which is a C _1-4 alcohol, to obtain a reaction mixture containing a 1,2-alkylenediol and a dialkyl carbonate ; And (vi) recovering 1,2-alkylenediol and dialkyl carbonate ≪ / RTI > delete 14. The process according to claim 13, wherein the alkanol is methanol, ethanol or isopropanol.

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